Operational experience with nanocoulomb bunch charges in the Cornell photoinjector

Bartnik, Adam; Gulliford, Colwyn; Bazarov, Ivan; Cultera, Luca; Dunham, Bruce

doi:10.1103/physrevstab.18.083401

Cited by 49 publications

(40 citation statements)

References 8 publications

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“…Further theoretical analysis and simulations show that this rf-coupler emittance growth can also be completely corrected with a weak rotated quadrupole. These quadrupole correction techniques for solenoids and rf couplers have been implemented into the LCLS-I and LCLS-II injectors as well as in the SwissFEL injector [25] and the Cornell dc photocathode injector [26].…”

Section: Discussionmentioning

confidence: 99%

Exact cancellation of emittance growth due to coupled transverse dynamics in solenoids and rf couplers

Dowell

Zhou

Schmerge

2018

Phys. Rev. Accel. Beams

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Weak, rotated magnetic and radio frequency quadrupole fields in electron guns and injectors can couple the beam's horizontal with vertical motion, introduce correlations between otherwise orthogonal transverse momenta, and reduce the beam brightness. This paper discusses two important sources of coupled transverse dynamics common to most electron injectors. The first is quadrupole focusing followed by beam rotation in a solenoid, and the second coupling comes from a skewed high-power rf coupler or cavity port which has a rotated rf quadrupole field. It is shown that a dc quadrupole field can correct for both types of couplings and exactly cancel their emittance growths. The degree of cancellation of the rf skew quadrupole emittance is limited by the electron bunch length. Analytic expressions are derived and compared with emittance simulations and measurements.

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Section: Discussionmentioning

confidence: 99%

Exact cancellation of emittance growth due to coupled transverse dynamics in solenoids and rf couplers

Dowell

Zhou

Schmerge

2018

Phys. Rev. Accel. Beams

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“…Therefore, for cathodes made from these elements, we expect to always have ≪ and q'/q=-1. 16 3.8x10 15 1.6x10 16 The dielectric function given in Eqn. (5) is a complex function whose real and imaginary parts are plotted in Figure 1.…”

Section: The Image Charge and The Dielectric Function Of Cathodesmentioning

confidence: 99%

“…The real part is plotted with the solid-red curves and the imaginary part is plotted using dash-blue curves. The plasma frequency is 1.64x10 16 rad/second and is the frequency where the real part is zero.…”

Section: Figure 1(color)mentioning

confidence: 99%

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Topological cathodes: Controlling the space charge limit of electron emission using metamaterials

Dowell

2019

Phys. Rev. Accel. Beams

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The space charge limit (SCL) of emission from photocathodes sets an upper limit on the performance of both high-and low-field electron guns. Generally, one is forced to strike a compromise between the space charge limit and the cathode's intrinsic emittance (I. Bazarov et al., Phys. Rev. Lett., 102,104801(2009)). However, it is possible to nearly eliminate the SCL due to the image charge by engineering the topography of the cathode's surface. A cathode with a surface plasma frequency below the frequency spectrum of the accelerating electrons will greatly reduce the bunch's image charge or polarization of the cathode, resulting in a small image-charge field. Thereby mitigating the cathode's space charge limit. In the work presented here, a theory for the image-charge field produced by a disk of charge being accelerated from the cathode surface is developed to include the frequency-dependent behavior of surface dielectric function on the fields seen by the beam. The paper applies this theory to mitigate the SCL of a novel cathode based upon a wire-array metasurface. It is shown that such meta-cathodes should have negligible space charge limits for photoelectric, thermionic and field emission.

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“…The high brightness, high repetition rate electron beams are key components for several scientific applications, such as X-ray Free Electron Laser (XFEL) [1,2] and Ultrafast Electron Diffraction/Microscopy (UEM/UEM) [3] when MHz-class repetition rates are required. Different types of electron guns have been under development for decades, such as the DC gun [4], the normal conducting RF gun [5] and the superconducting RF gun [6], each with its own advantages and challenges. In the Advanced Photoinjector EXperiment (APEX) at Lawrence Berkeley National Laboratory (LBNL), a photoelectron gun based on a normal conducting re-entrant RF cavity operated at Very-High-Frequency (VHF) 185.7 MHz (1/7th of 1.3 GHz), has been designed, manufactured and commissioned [7].…”

Section: Introductionmentioning

confidence: 99%

RF design of APEX2 two-cell continuous-wave normal conducting photoelectron gun cavity based on multi-objective genetic algorithm

Luo

Feng

Filippetto

et al. 2019

Nuclear Instruments and Methods in Physics Research Section A:

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High brightness, high repetition rate electron beams are key components for optimizing the performance of next generation scientific instruments, such as MHz-class X-ray Free Electron Laser (XFEL) and Ultra-fast Electron Diffraction/Microscopy (UED/UEM). In the Advanced Photo-injector EXperiment (APEX) at Berkeley Lab, a photoelectron gun based on a 185.7 MHz normal conducting re-entrant RF cavity, has been proven to be a feasible solution to provide high brightness, high repetition rate electron beam for both XFEL and UED/UEM. Based on the success of APEX, a new electron gun system, named APEX2, has been under development to further improve the electron beam brightness. For APEX2, we have designed a new 162.5 MHz two-cell photoelectron gun and achieved a significant increase on the cathode launching field and the beam exit energy. For a fixed charge per bunch, these improvements will allow for the emittance reduction and hence to an incresed beam brightness. The design of APEX2 gun cavity is a complex problem with multiple design goals and restrictions, some even competing each other. For a systematic and comprehensive search for the optmized cavity geometry, we have developed and implemented a novel optimization method based on the Multi-Objective Genetic Algorithm (MOGA).

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Operational experience with nanocoulomb bunch charges in the Cornell photoinjector

Cited by 49 publications

References 8 publications

Exact cancellation of emittance growth due to coupled transverse dynamics in solenoids and rf couplers

Exact cancellation of emittance growth due to coupled transverse dynamics in solenoids and rf couplers

Topological cathodes: Controlling the space charge limit of electron emission using metamaterials

RF design of APEX2 two-cell continuous-wave normal conducting photoelectron gun cavity based on multi-objective genetic algorithm

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